Atomic distribution of alloying elements and second phase particles (SPPs) identification in Optimised ZIRLO

The accurate chemical composition of second phase particles (SPPs) and solute distributions at grain boundaries and interfaces are still not known for Optimised ZIRLO, with recent debate over the identification of a Zr-Nb-Fe intermetallic phase in these alloys. Here, atom probe tomography (APT) is combined with scanning transmission electron microscopy (STEM), transmission Kikuchi diffraction (TKD), and density functional theory (DFT) to demonstrate that the phase, commonly reported as Zr(Nb,Fe) 2 , is most likely an intermetallic phase of (Zr,Nb) 3 Fe with ∼35 at.% Nb. Interfacial excess is calculated at the β-Nb/α-Zr and (Zr,Nb) 3 Fe/α-Zr interfaces and at the grain boundaries. Fe is enriched at the interface between β-Nb precipitates and the α-Zr matrix. Fe, Sn, and Nb segregate at α-Zr grain boundaries, no Sn segregation was observed at the interface of β-Nb/α-Zr matrix, and slight Sn segregation was detected at the interface of the intermetallic phases with the α-Zr and at the grain boundaries. An enhanced understanding of grain boundary segregation, secondary phases composition, and solute behaviour will inform a better understanding of mechanical and corrosion properties, which is expected to be useful for future Zr alloy development.